A heat exchanger of the present invention comprises: a mixture inflow unit into which a mixture of air and fuel is introduced; a burner for combusting the mixture introduced through the mixture inflow unit; a sensible-heat exchange unit that is disposed around the burner such that heat is exchanged between combustion gas caused by the combustion of the burner and a heating medium, and is constituted with a plurality of unit plates stacked on each other; a latent-heat exchange unit in which heat is exchanged between the combustion gas having passed through the sensible-heat exchange unit and a heating medium and which is constituted with a plurality of unit plates stacked on each other; and a combustion gas discharge unit for discharging the combustion gas having passed through the latent-heat exchange unit, wherein a heating medium passage, a combustion gas passage, and a combustion gas discharge passage that connects the combustion gas passage and the combustion gas discharge unit are formed in the interior
